Method for producing catalytically-active materials

ABSTRACT

A method for producing a catalytically-active material having at least one base component and at least one catalytically-active component in which the at least one base component is heated to a softening or melting temperature to form a softened or molten base component. While the base component is in the softened or molten state, at least one catalytically-active component is incorporated into or onto the base component, forming the catalytically-active material. In accordance with one embodiment, a catalyst precursor is introduced into the base component and subsequently transformed to a catalytically-active component.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 11/075,018 filed 8 Mar. 2005, now U.S. Pat. No. 7,449,424,which claims the benefit of provisional U.S. patent application Ser. No.60/571,379 filed 14 May 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a general method for creating robust,catalytically-active materials suitable for use in a variety ofapplications. The catalytically-active materials of this invention areengineered to resist attrition or to exhibit controlled rates ofattrition in a variety of host environments. These applications include,but are not limited to, petroleum refining, Fischer-Tropsch syntheses,chemical synthesis and production, including the synthesis andproduction of pharmaceutical compounds, the production of plastics andfoodstuffs, and catalysts that effect a chemical or physical change incombination with complexes of DNA-related molecules or living organisms,such as natural or genetically modified bacteria. This invention furtherrelates to catalysts and catalytically-active materials suitable for usein gasification reactor vessels, in particular fluidized bedgasification reactor vessels, and combustion processes. Finally, thisinvention relates to a method and apparatus for reducing or eliminatingtars, which are typically defined as organic compounds having amolecular weight equal to or greater than 78, for example, benzene, andother undesirable volatile compounds produced during the gasification ofvarious feedstocks including coal, biomass and waste materials and thecombustion of various fuels.

2. Description of Related Art

In general terms, gasification is a process whereby solid carbonaceousmaterials such as coal and biomass are converted into cleaner-burninggaseous fuels. Gasification is frequently carried out in a fluidized bedreactor, a reactor chamber comprising a fluidized bed support disposedwithin the reactor chamber and a fluidized bed material disposed on thefluidized bed support, which fluidized bed material comprises an inertcomponent that is either fully inert or has low catalytic activity, anda catalytically-active component that is dispersed within or upon theinert component. During the gasification process, numerous by-products,including tars and other volatile materials, are also generated.Environmental regulations require that these by-products be treated orotherwise disposed of in an environmentally acceptable manner.

Catalysts are recognized as being essential for reducing or eliminatingthe tars that accompany the gasification of solid materials. Robust,efficient catalysts that are added to or comprise the bed material offluidized bed gasifiers represent a significant development because theyreduce the overall gasifier footprint by virtue of their incorporationinto the gasifier, offer the possibility of substantially eliminatingtar formation, and retain their activity in a harsh, chemically activeenvironment. However, the development of in-bed catalysts has been slowbecause, to date, mineral geology has been relied upon for selection ofthe best materials for catalyst development. Thus, the ability to moveaway from earth mineralogy as the basis for identifying and selectingsuitable materials is a highly desirable objective, opening the door tothe development of new catalyst formations from present waste materials,such as arc furnace dust, mold sands, various slags and mill scale.

Catalytically-active materials employed for reducing or eliminating tarsthat are produced in the gasification of coal, biomass, or othermaterials, as well as for other applications, typically comprise twofundamental components, a catalytically-active component and a base orsubstrate component for support of the catalytically-active component.The base or substrate component is a material substantially physicallyand chemically inert to the environment in which it is to be used and istypically either a solid monolithic structure wherein thecatalytically-active component is deposited onto the surface of thestructure or a porous structure wherein the catalytically-activecomponent is disposed on the surface of the structure and in the poresof the structure.

At the present time, most catalysts are prepared by depositing thinlayers of catalytically-active materials onto rigid, attrition-resistantsubstrates or by coating rigid, refractory monoliths (typically used ina self-supporting off-bed tar-cracker or specialized support structurefor chemical synthesis). Typical substrates include α-alumina andzirconia. The method of applying a catalytically-active layer onto aninert support varies, but generally two approaches are employed. Themost common method, the incipient wetness or wet impregnation method, istypically accomplished by immersion of the substrate in an aqueoussolution of a catalyst precursor (typically a metallic salt), resultingin a coated substrate, followed by heating of the coated substrate toconvert the catalyst precursor to a catalytically-active material,typically a metallic oxide. If the substrate is porous, a so-calledthree-dimensional or 3-D catalyst is created. If the surface is notporous, a two-dimensional or 2-D catalyst is created.

Another recently developed method for preparing catalysts uses thermalplasma chemical vapor deposition or TPCVD. This method is primarily usedto produce monolithic two-dimensional catalysts and involves spraying aconcentrated solution of a metallic salt through a plasma torch onto asuitable refractory substrate. Thus, the end product is a catalystcomprising an inert, rigid substrate with a thin, catalytically-activeouter layer. If the outer layer is damaged through attrition orfragmentation, overall catalytic activity is reduced. However, theadvantage of this approach is that relatively large amounts of highsurface area catalysts that incorporate precious metals can be producedwith minimal amounts of these materials.

Two routes are generally available for employing catalysts to reduce oreliminate tars that are produced during the gasification of coal,biomass, or other materials. The first route is through the use ofcatalysts as described above disposed on the surface of otherwise inertmonolithic substrates, which are disposed downstream of the gasificationreactor vessel so that the gasification product gases are exposed to thecatalysts. Typical of such catalysts are oxides of nickel, cerium,ruthenium, and lanthanum. Catalytic materials have also been embeddedinto ceramic candle filters so that during high temperature gas particleseparation, intimate gas-catalyst contact is assured.

The second route is through the direct introduction of suitably smallfragments or beads of catalytic materials into the bed of afluidized-bed gasifier. These catalytically-active materials are eitherprepared by depositing a catalyst onto an inert, abrasion-resistantsubstrate, either monolithic or porous, or are available asnaturally-occurring minerals that exhibit catalytic activity. Dolomiteand olivine are examples of this type of naturally occurring material.When properly sized fragments of dolomite or olivine are added to thebed of a fluidized bed gasifier, they become intimately involved in thegasification process, achieve good contact with raw fuel gases andinhibit tar formation by cracking or reforming the tars as they areproduced to generate lower molecular weight hydrocarbons and carbon.However, a long recognized problem with dolomite is that within the bedof a gasifier, dolomite is rapidly calcined. Calcined dolomite isfriable and, thus, tends to be quickly milled within the bed until itsparticle size becomes too small to be retained within the reactorvessel. This creates the need to replace the attrited catalyst andproduces undesirable waste particulate material, aside from ash, thatmust be separated from the fuel gas. Thus, there is a need for durablecatalytic materials that can withstand fluidized bed temperatures andresist fragmentation or, at a minimum, abrade at a slow, predictablerate so that fresh catalyst remains available.

As previously stated, in addition to dolomite, olivine is a naturallyoccurring catalytic material suitable for reducing tars in fuel gas.Olivine, which is a very hard, attrition-resistant, glassy materialwhich has a very high melting point (1760° C.) and which exhibitscatalytic activity for tar removal with extended heat treatment in airat about 900° C., is actually a mixture of two minerals—Fe-rich fayalite(Fe₂SiO₄) and Mg-rich forsterite (Mg₂SiO₄). Untreated, naturallyoccurring olivine exhibits less activity for tar removal than dolomite.However, it has been found that heating olivine for extended periods inair at about 900° C. appears to provide sufficient mobility to ironwithin the olivine so that it becomes enriched at the olivine-airinterface. Free iron at the olivine-air interface is then transformedinto an oxide by reacting with oxygen in the air and olivine that hasbeen prepared in this manner has been found to exhibit enhancedcatalytic activity for reducing tars in biomass-derived fuel gas. Inaddition, the catalytic activity of olivine is further enhanced bycalcining at 1100° C. olivine that has been treated with an aqueoussolution of Ni(NO₃)₂·6H₂O to a level of about 2.8 weight percent nickelcontent when dry. By virtue of this treatment, a very activeolivine-based catalyst is produced that contains abundant quantities ofNiO on the surface of finely divided olivine that has been sized to bein the range of about 250 μm to about 600 μm. Calcining at either higheror lower temperatures appears either to drive the NiO into the olivineor restrict adhesion of NiO to the surface of the olivine. This methodof preparing a NiO-based catalyst on an olivine support is taught, forexample, by International Patent Publication No. WO 01/89687 A1.

SUMMARY OF THE INVENTION

It is, thus, one object of this invention to provide acatalytically-active material suitable for use in harsh environmentssuch as those found in gasification reactor vessels and combustionsystems.

It is another object of this invention to provide a catalytically-activematerial that is attrition-resistant.

It is a further object of this invention to provide a method forproducing a catalytically-active material suitable for use in the harshenvironments of gasification reactor vessels and combustion systems.

It is yet a further object of this invention to provide acatalytically-active material for reducing or eliminating tars and othervolatile compounds as they are generated in gasification and combustionprocesses.

It is still another object of this invention to provide a method andapparatus for in-situ reduction or elimination of tars and othervolatile compounds generated in gasification and combustion processes.

These and other objects of this invention are addressed by a method forproducing a catalytically-active material having at least one basecomponent, which base component is substantially chemically and/orphysically inert to the environment of intended use of thecatalytically-active material, and at least one catalytically-activecomponent, in which the at least one base component is heated to asoftening temperature or melting temperature and the at least onecatalytically-active component or at least one catalyst precursorcomponent is incorporated into the softened or molten base component,thereby forming a catalytically-active softened or molten material or acatalyst precursor softened or molten material. In accordance with theembodiment in which the catalytically-active component is incorporatedinto the softened or molten base component, the resultingcatalytically-active softened or molten material is then solidified,typically by cooling, resulting in the desired catalytically-activematerial. One of the significant benefits of producing acatalytically-active material in accordance with this embodiment of themethod of this invention is the ability to use catalytically-activematerial directly in contrast to conventional methods for producingcatalysts in which a substrate or base component is coated with acatalyst precursor and then heated to convert the catalyst precursor toa catalytically-active material. In accordance with the embodiment inwhich the catalyst precursor is incorporated into the softened or moltenbase component, the catalyst precursor is chemically reacted, e.g. withoxygen, to form a catalytically-active material. The chemical reaction,which is carried out by exposing the catalyst precursor component to anenvironment that facilitates the chemical transformation, may occurbefore, during or after the catalyst precursor softened or moltenmaterial is solidified.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

The invention claimed herein is a method for producing catalysts orcatalytically-active materials comprising a substantially inertcomponent, or base component, and a catalytically-active component, inwhich the catalytically-active component is directly incorporated intothe base component or in which a catalyst precursor material isincorporated into the base component after which the catalyst precursormaterial is chemically transformed to produce the catalytically-activecomponent. As used herein, the term “catalyst precursor” refers to amaterial which, upon exposure to a suitable environment, undergoes achemical transformation to form a catalytically-active component. Anexample of a catalyst precursor is a metal such as Ni, which, whenexposed to oxygen, oxidizes to form the catalytically-active materialNiO. As previously indicated, catalyst substrates are typically madefrom refractory ceramics and catalytic materials are often made fromrefractory metal oxides. Thus, methods of manufacture which seek toprocess the substrate and the catalyst into one material must carry outsome processing steps at very high temperatures. Although the method ofthis invention may be used to produce catalysts for use in a variety ofapplications as mentioned herein above, it is particularly suited forproducing catalysts suitable for use in harsh environments such as theenvironment found in gasification reactor vessels.

In accordance with one embodiment of the method of this invention, asubstantially chemically inert, durable, attrition-resistant basecomponent is heated to a softening or melting temperature, producing asoftened or molten base component. At least one catalytically-activecomponent is then incorporated into the softened or molten basecomponent and then solidified to produce a catalytically-activematerial. The solidified catalytically-active material is then processedto put it into a form suitable for use in its intended application.

In accordance with one embodiment of this invention, the substantiallychemically inert, durable, attrition-resistant base component is heatedto a softening or melting temperature, producing a softened or moltenbase component, and at least one catalyst precursor is then incorporatedinto the softened or molten base component, in which it undergoes achemical transformation to form the desired catalytically-activematerial. This chemical transformation may take place before, during orafter the softened or molten material has been solidified and processedto put it into a form suitable for use in its intended application.Without wishing to be bound by any single mechanism by which thecatalyst precursor is transformed into a catalytically-active material,it is believed that the catalyst precursor material is mobile in certainglassy materials or in glass ceramics, constantly migrating through thebase component to maintain or refresh the catalytic activity at thesurface of the catalytically-active material. When exposed to oxygen atthe interface between the surface of the catalytically-active materialand the surrounding environment, the catalyst precursor may betransformed to the desired catalytically-active material.

For use in a fluidized bed gasification reactor, thecatalytically-active material formed in accordance with the method ofthis invention is formed into substantially uniform sized shards orspheres. This may be accomplished by any means known to those skilled inthe art, such as mechanical grinders and ball mills. In accordance withone particularly preferred embodiment of this invention, thesubstantially chemically inert, durable, attrition-resistant basecomponent is a glassy, amorphous material. As used herein, the term“glassy” refers to materials having the characteristics of glass,including glass ceramics. These glasses are able to withstand theenvironment of a fluidized bed gasifier for extended periods of time.

In accordance with one embodiment of this invention, thecatalytically-active material is produced in a manner which enables slowattrition within the fluidized bed so that fresh catalyst is availableas required. These particles are prepared in a manner which enables themto be added to the material in the fluidized bed gasifier or, ifsuitable, to be utilized as all of the fluidized bed material in thefluidized bed gasifier. Thus, depending upon the level of catalyticactivity desired, the uniformly shaped shards or beads ofcatalytically-active material can serve either as part of or all of thefluidized bed material.

In accordance with one embodiment of this invention, catalyticprecursors distributed throughout the base component becomecatalytically active upon exposure to the environment within thegasifier.

In accordance with another embodiment of this invention, the basecomponent comprises a glassy material that allows suspended metals oralloys or very small catalytically-active particles or suspendedcatalyst precursors (metals, semi-conductors, or alloys or compounds ofsuch components) dispersed within the glassy material to migrate to thesurface of the catalytically-active material so as to refresh orincrease the catalytically-active component present at the surface ofthe catalytically-active material. In accordance with yet anotherembodiment of this invention, the catalytically-active material and/orthe catalyst precursor material is in the form of foams that can bemolded into rigid monoliths or mechanically dispersed or formed intocatalytically-active particles of a size appropriate for a particularprocess. In accordance with still a further embodiment of thisinvention, the catalytically-active material and/or the catalystprecursor material may be formed into fibers using techniques known tothose skilled in the art for producing rock wool or fiberglass. Thefibers can be aggregated to form barrier filtration devices that canboth filter and catalytically transform compounds present in a liquid orgas carrier medium.

In addition to use as fluidized bed material for in situ reduction orelimination of tars generated by a gasification process, other catalystformulations may be formed in accordance with the method of thisinvention, such as catalysts that reduce or bind alkali materials andcatalysts that reduce or bind halogen compounds. In addition tofluidized bed applications, catalysts for reducing tars in accordancewith this invention may be made into high surface area monoliths, thatis, glasses fused to alumina or zirconia monoliths, which are thenexposed to fuel gases, i.e. gasification products exiting the gasifier.These materials may also be added as finely divided particles to fuelgas exiting the gasifier so that they are caught on and within a dustcake of a particulate collection device and continuously recycled orrefreshed as needed when the particulate collection device is cleaned.

Still further applications of the catalytically-active material of thisinvention include catalytically-active heat resistant coatings for useat the entrance to high temperature fuel cells and for the entrances,blades or interior surfaces of gas turbines. These materials may also beused as coatings for the insides of pipes, either integrated intorefractory linings or applied to the inside surface of the pipes, tominimize deposition of tars and other materials. Materials containingcatalysts in accordance with this invention may also be used to treatdiesel exhaust, presuming that catalysts to increase carbon utilization(through combustion) and volatile organic compounds (VOC) destruction(through catalysis) could be placed within combustion chambers or inexhaust manifolds.

In accordance with one particularly preferred embodiment of thisinvention, the substantially inert, base component of thecatalytically-active material produced in accordance with the method ofthis invention is olivine and the catalytically-active component is ametal or metal oxide selected from the group consisting of Al, Ag, Au,Ca, Co, Cr, Cu, Eu, Fe, Gd, Ir, La, Mg, Mn, Ni, Pr, Pt, Ru, Rh, Sn, Zn,and alloys and mixtures thereof. For particulate material to be suitablefor use as the inert component of a fluidized bed requires formation ofparticles having sizes suitable for use in fluidized bed reactors,preferably in the range of about 250 μm to about 600 μm, anddistribution of the catalytically-active components within the inertcomponent particles. Conventional glass melters and iron meltingprocesses operate at temperatures below the melting point of olivineand, thus, generally are not suitable for use in the method of thisinvention. However, any process which produces sufficient temperature tomelt “black” glass may be utilized in the method of this invention.Glass melters satisfying this criteria include submerged combustionmelters, induction melters, plasma melters, and immersed tube melters.Due to the intimacy of contact between the burner output of a submergedcombustion melter and the material being melted, submerged combustionmelting is a particularly suitable process for producing softened ormolten materials comprising catalytically-active materials and/orcatalyst precursor materials in accordance with the method of thisinvention.

The concept of submerged combustion is not new and burners suitable foruse in the melting of high melting temperature materials, such as glass,metals, etc. are also known. See, for example, U.S. Pat. No. 3,260,587to Dolf et al., which teaches a method and apparatus for submergedcombustion melting of glass or similar materials in which a burnerhaving an air cooled casing is inserted into a furnace wall, either thefurnace side wall or the furnace floor. The burner is provided withmeans for mixing fuel gas and air, burning them and discharging thecombustion products at high temperature and velocity into the glass. Thehot gases agitate the glass, transferring a high percentage of heat tothe glass, thereby rapidly melting the glass. U.S. Pat. No. 3,738,792 toFeng describes a burner for use in submerged combustion applicationswhich is able to use liquid fuels. Thus, by virtue of the intimatecontact that occurs between the combustion products and the molten glassor other molten materials, submerged combustion melters are able tooperate at substantially higher temperatures than conventional melters.

Accordingly, fluidized bed materials suitable for use in in-situreduction or elimination of tars and other volatiles generated duringgasification of coal, biomass and waste materials may be produced bymelting olivine or another suitable glassy material in a submergedcombustion melter, forming a molten glass, and introducing a material ina form suitable for forming a catalytically-active component, e.g. afinely divided powder of NiO, into the submerged combustion melter,resulting in distribution of the catalytically-active component withinthe molten material or a catalyst precursor component, e.g. a metal thatoxidizes to form a catalytically-active material. Once thecatalytically-active material or catalyst precursor material has mixedwith the melt, it can then be processed by any suitable glass-formingprocess and drawn into fibers or formed, as a molten material, into amolded monolithic product, as a solid or foam, as fragments of foam, oras small spheres, flakes, shards, or specially-shaped fragments ofcatalytically-active material or catalyst precursor material, before oras it is cooled. Alternatively, after refining and subsequent removal ofthe refined fluidized bed material from the melting operation, thecooled material may be subjected to any of a number of techniques knownto those skilled in the art for producing the desired material particlesizes, for example, mechanical fragmentation, fritting, and chemicalmilling.

In accordance with one embodiment of this invention, thecatalytically-active material and/or the catalyst precursor can be addedto the melt outside the melter, by any of several means, while thematerial is still soft or molten, so that it becomes disproportionatelyembedded or enhanced in the outer layers of the foam, fragments, beadsor shards produced. This can be accomplished by adding material duringthe melting process at a temperature between the so-called working pointand the so-called softening point of the melted material. Working pointsand softening points vary for different glasses, but are usually around1000° C. and 650° C., respectively. Because olivine melts at about 1760°C., much higher than common glasses, the working and softening points ofthis material would be higher.

In accordance with one embodiment of this invention, the molten basecomponent, infused with catalytically-active material and/or catalystprecursor material, is solidified by rapid quenching upon removal fromthe glass melter to form amorphous glasses that may be more amenable tosubsequent mechanical or chemical processing than similar material thatis more slowly cooled.

In accordance with one embodiment of this invention, the substantiallyinert base component of the catalytically-active material produced inaccordance with the method of this invention is a metal and thecatalytically-active component is any catalytically-active refractorymetal alloy, oxide, or compound that when added to the molten orsoftened inert base metal retains its catalytic activity. For a metal tobe suitable for use as the inert component of a catalytically-activematerial requires that it be inert to the process and be amenable tobeing worked or formed into arbitrary shapes, monoliths, and particlesthat exhibit catalytic activity. Suitable metals include iron, copper,and aluminum. For a fluidized bed, standard metal forming techniqueswould be used to produce particles of the catalytically-active materialhaving sizes suitable for use in fluidized bed reactors, preferably inthe range of about 250 μm to about 600 μm, and distribution of thecatalytically-active components within the inert component particles.

Although this invention has been described primarily in connection withhigher softening and melting temperature base components andcatalytically-active components suitable for use in relatively hightemperature application, there are other catalytically-active materialswhich may be produced in accordance with the method of this invention,and such materials are deemed to be within the scope of this invention.By way of examples, suitable base components include organic polymerssuch as RYTON, nylon, rayon, NEXTEL, MYLAR and waxes.

While in the foregoing specification this invention has been describedin relation to certain preferred embodiments thereof, and many detailshave been set forth for the purpose of illustration, it will be apparentto those skilled in the art that the invention is susceptible toadditional embodiments and that certain of the details described hereincan be varied considerably without departing from the basic principlesof this invention.

1. A method for producing a catalytically-active material having atleast one base component and at least one catalytically-active componentcomprising the steps of: heating said at least one base component to asoftening temperature, said at least one base component comprising aglass ceramic, forming a softened base component; incorporating said atleast one catalytically-active component into said softened basecomponent, forming said catalytically-active material; and solidifyingsaid catalytically-active material.
 2. A method in accordance with claim1, wherein said at least one catalytically-active component comprises atleast one of a metal and a metal oxide.
 3. A method in accordance withclaim 2, wherein said metal and said metal oxide comprise a metalselected from the group consisting of Al, Ag, Au, Ca, Co, Cr, Cu, Eu,Fe, Gd, Ir, La, Mg, Mn, Ni, Pr, Pt, Ru, Rh, Sn, Zn, and alloys andmixtures thereof.
 4. A method in accordance with claim 1, wherein saidat least one catalytically-active component comprises a catalyticmaterial suitable for reducing volatiles generated by at least one of agasification process and a combustion process.
 5. A method in accordancewith claim 1, wherein said at least one base component is heated in asubmerged combustion melter.
 6. A method in accordance with claim 5,wherein said at least one catalytically-active component is incorporatedinto said at least one base component directly in said submergedcombustion melter.
 7. A method for producing a catalytically-activematerial comprising the steps of: heating at least one base componentcomprising a glass ceramic to a softening temperature, forming asoftened base component; incorporating at least one catalyst precursorinto said softened base component, forming a catalyst precursormaterial; and transforming said at least one catalyst precursor into acatalytically-active component, forming a catalytically-active material.8. A method in accordance with claim 7 further comprising solidifyingsaid catalyst precursor material.
 9. A method in accordance with claim 7further comprising solidifying said catalytically-active material.
 10. Amethod in accordance with claim 7 further comprising incorporating atleast one catalytically-active component into said softened basecomponent.
 11. A method in accordance with claim 7, wherein said atleast one catalytically-active component comprises at least one of ametal and a metal oxide.
 12. A method in accordance with claim 11,wherein said metal and said metal oxide comprise a metal selected fromthe group consisting of Al, Ag, Au, Ca, Co, Cr, Cu, Eu, Fe, Gd, Ir, La,Mg, Mn, Ni, Pr, Pt, Ru, Rh, Sn, Zn, and alloys and mixtures thereof. 13.A method in accordance with claim 7, wherein said at least one basecomponent is heated in a submerged combustion melter.
 14. A method forproducing a catalytically-active glass ceramic comprising the steps of:heating a glass ceramic to a softening temperature, forming a softenedglass ceramic; incorporating at least one catalytically-active materialinto said softened glass ceramic, forming a catalytically-active glassceramic; and solidifying said catalytically-active glass ceramic.